1. Field of the Invention
The present invention relates to an object, a method, or a manufacturing method. In addition, the present invention relates to a process, a machine, manufacture, or a composition of matter. One embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a memory device, a driving method thereof, or a manufacturing method thereof. In particular, one embodiment of the present invention relates to a semiconductor device, a display device, or a light-emitting device each including an oxide semiconductor.
In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A display device, an electro-optical device, a semiconductor circuit, and an electronic appliance include a semiconductor device in some cases.
2. Description of the Related Art
A semiconductor device such as a programmable logic device (PLD) or a central processing unit (CPU) has a variety of configurations depending on its application. The semiconductor device generally includes a memory device; the PLD includes a register and a configuration memory, and the CPU includes a register and a cache memory.
These memory devices need to operate at higher speed in writing and reading data than a main memory for which a DRAM is generally used. Thus, in many cases, a flip-flop is used as a register, and a static random access memory (SRAM) is used as a configuration memory and a cache memory.
The SRAM achieves high-speed operation with miniaturization of a transistor; however, there is a problem in that as the transistor is miniaturized, an increase in leakage current becomes obvious, which results in increased power consumption. In order to reduce power consumption, an attempt has been made to stop the supply of a power supply potential to a semiconductor device in a period during which data is not input or output, for example.
However, a flip-flop used as a register and an SRAM used as a cache memory are volatile memory devices. Therefore, in the case where the supply of a power supply potential to a semiconductor device is stopped, data that has been lost in a volatile memory device such as a register or a cache memory need to be restored after the supply of the power supply potential is restarted.
In view of this, a semiconductor device in which a nonvolatile memory device is located on the periphery of a volatile memory device has been developed. For example, Patent Document 1 discloses the following technique: data held in a flip-flop or the like is backed up in a ferroelectric memory before the supply of a power supply potential is stopped, and the data backed up in the ferroelectric memory is restored to the flip-flop or the like after the supply of the power supply potential is restarted.    [Patent Document 1] Japanese Published Patent Application No. H10-078836